Crystallization Fouling With Enhanced Heat Transfer Surfaces

Abstract

The aim of this paper is to demonstrate that a simple stirred batch cell can be used to study the effects of surface shear stress (among other process parameters) on fouling from saturated calcium salt solutions. For otherwise identical operating conditions, the overall fouling rate on a smooth mild steel surface was found to be reduced either when fine wires were attached to it or when helical threads were incorporated into the surface, either in the form of a continuous helical groove or in the form of a raised helix. The raised helical surface was more effective in reducing fouling than the helical groove. The results confirm the general effect that fouling rates can be reduced by increasing the surface shear stress through surface enhancement. A simple mathematical model has been developed to take into account the dynamic change in bulk concentration as crystallization fouling occurs. In all cases, the overall fouling resistance increased asymptotically toward a constant value and could easily and accurately be described quantitatively by the new analytical model. The variations of shear stresses on the various surfaces were determined from computational fluid dynamics simulations using the commercial package Comsol 4.2.